Radio relay system



Sept. 20, 1932. F. CONRAD RADIO RELAY .SYSTEM Filed Jan. 28, 1926V 5 Sheets-Sheet Q w DH.

Sept. 20, 1932. F, CONRAD 1,877,815

RADIO RELAY SYSTEM Fled Jn. 28, 1926 3 Sheets-Sheet 2 From /44 oscillmb WITNESSES: Gen- Q- INVENTOR F ran/f onmd uw 3% 8L wf, u,

.,- ToR'NEY Sept. 20, 1932. F. CONRAD RADIO RELAY SYSTEM Filed Jan. 28, 1926 3 Sheets-Sheet 3 INVENTOR FranK Conrad wnNEssEs; RJ. )16M A'TTORNEY `raiemed sept. zo, 1932 TTQES FRANK CONRAD, or rrrrsnunerr, PENNsvLvANiA, AssrGNon To WnsrrNGi-rousn ELECTRIC &` `MANUFACTURING COMPANY, A conr'oRAroN or ruinas,YrivAirnii uAppiieafimi med January 28,1926. serial No. al1-,341@` vMy.inventionrelates to the art of radio transmission and reception audit has particular reference to what are `knovvn as relay systems in `which signals received `from disf tant points are used tocontrol the operation oiga local transmittingst'ation. i A

Numerous systems of this type have been `propose-d heretofore, all of Which,in so farL as I am aware, involve the reduction of the incoming signal `to an audio' frequency, which,

inturn, is used to modulate the output of an i oscillation generator ofthe radiation circuit.

`Such systems have numerous disadvan tages. i It a single superpower station isdemployed to Control a plurality of relay stations, ituhas been found necessary, in order to avoid Ainterference between the various stations, to jso arrange each separate station'that itA will radiate on a Wave length which differs Widely from that of the nextinearest station. This naturally handicaps the company Aoperating the `chain of relay stations `as thenumber of available Wave lengths is necessarily limited. At the same time, such a system necessitates constant engineeringattention in order that `the radiated Wave length may beheld Within the required limits of variation. Again, in theusual type of relay system,the receiving antenna tends topick up a portion ofthe energy radiated from thelocal transmitter,

resulting in unsatisfactoryreception from` the distant station. y A o Interference from' static land' from' other stations operating on Wave lengths close to those `of the master stationalso cause numerf ous diiiiculties, With the result Athat no' satisi i factory type of relay system other than mine has, as yet, gone into extensive use.

One ofthe ob]ects of my inventiomaccordingly, is to provide a` relay` system `Which "will i not `be subjectto the.` Vdisadvantages mentioned aboveand `vvlmich will, `at all times,

be substantiallyautomatic irl-operation,` re- Y 45 quiring minimum supervlslon.

,Another objectfsto devise a system lWhich `will clearly ,reradiatef with freedom" from j power interiereiice,\static interference or` in"- t `teriz'erenice .picked-.up from other yroadcasting stations. i l 1 Another object of my invention is topro- Widely separated geographically from `the local` transmitting station, communication therebetween being maintainedby means of 1 land lines, over which the signals controlling the transmitter are sent. 3 l

A further object of my invention `is to provide a receiving system which will be stable in operation, which Will automatically compensate forlosses occurring in the antenna, and which Will insure thereradiation of a wave of practically constant frequency.

A still further object of my invention is to reradiate the programs or other ,Y signals on the same Wave length as that used by the master station, thus preventing interference between the various relay stations.

My invention, briefly stated,l may be b est characterized as a novel application of a radio-frequency amplifier. The incoming signals are picked up on a highly directive antenna system, rst amplified ina receiver, which may be regenerative, and may employ the zero beat principle of reception, then further amplified in an amplifier Which is carefully adjusted to prevent local oscillations, and transferred from this amplier to Wires leading to the local transmitting station.` At the local station, the signals are still further amplified in amplifiers using tubes of progressively increasing power, and

finally reradiated into spaceat the frequency atwhich they are received.

i The radiating structure is also made highly directional, the line of `maximum transmission being approximately parallel to `the line of best reception of the receiving an tenna system, which, together with `a rotatable loop at thereceiving station, is used to balance ,out signals from the local transmitting station, v.and prevents,` to -a large degree,` the local receiver from Vpicking up such signals. i

The receiving amplifier may be controlled as to frequencybya `pieno-electric crystal oscillator, which, also compensates for `antennae losses;` Undesired signals are prevented i'rom affecting the Flinesbetvv'een the receiving andtransmitting stations' by keeping both of these lines at the same potential with reference to ground, while interference between the various units at the transmitting station is prevented by'a novel use of what might be termed a balanced or pushpull amplier so'arranged that theconnecticnsfleading ti ereto VVare aected by dis- Vturbances in such manner vthat they will canmay be had:

` frequency amplifier situated at the receiving station.

Fig. 5 illustrates diagrammatically the am-V plifier at the transmitting station and shows in detail the balancing arrangement referred to above. i

Fig. 6 illustrates a modification of the arrangement in which the balancing loop may be vconneetedto the transmission line between `'receivingantenna system andV receiving ampliier. Y Y

VF ig. 7 showsa crystal-controlled oscillation generator whichl employ; and

` Y Fig. 8 illustrates a modifiedsystem in which the first tube shown in Fig. 4 may be controlled by the oscillation generator in Fig. 7. Referring now specifically to Fig. 1, the preferred form of my complete relay system fis therein vshown diagrammatically The antenna counterpoise system 1, 2 is conductively connected to VanV inductance 3 which, in turn, is coupled-to another inductance 4. The inductance 4 is connected by leads 5 to an inductance 6, )which is coupled to another l inductance 7 both of the latter inductances ybeing a part of the receiving station amplier indicated by rectangle 9. A balancing loop '10'is rotatable on avertical axis. This loop is adapted to be tunedV by' a condenser 11.

` Shuntedacrloss'V this tuning condenser is an `inductance 12 Vwhich is coupled to another.

inductance 13 whichris VVconnected across the leads 5 to the receiving station amplifier previously described. I Y f An inductance 14 in the output circuit of this amplifier 9 is coupled'to an inductance lrfrom which lead the land lines 16. These Vland lines are shownv as broken, indicating that the transmitting station may be lgeo'- graphicallysituated somedistance away from the'receiving`station.V The land lines 16'are lconnected Ato an inductance V18 which forms the input circuit ofV an ampliiier indicated of a prei by rectangle 19`located at the transmitting station. Y

An inductance 20 inthe output circuit of the amplifier 19 is coupled by means of condensers 21 and 22 to an inductance 23 which formsthe input circuit of a balancedpower ampliiierindicated by rectangle 24.V Coupled to amplifier 24"by means of lead v275 and condenser 26, is a power amplier, indicated by rectangle 27. l Thispower amplifier, which may compriseV a plurality of Vhigh-power, water-cooled tubes, feedsa tank circuit comprising aY condenser 28 and inductance 29.

VThis tank 'circuit is coupled through a condenser 30 to the radiating system 31. n

fF ig. shows a preferred arrangement of receiving and transmitting antennae with reference to the source of signals. The receiving antennae 1 are'spaced along a line A-B normal to the direction from'which the signals are to be received, the direction of best reception of the receiving'antennae being shown by a polar diagram 32. The balancing loop 10 vertical antennae 1,v 1, 1, 1 as well as Vacorre-V sponding number of vertical counterpoise elements 2, 2, 2,72 are shown as supported on poles spaced along a line A*B normal tothe direction from which desired signals arrive- Each antenna-counterpoise unit is separated a distance equal to one-third of a wave length from the next antenna-counterpoise unit and the total'distance between the extreme elements is made equal to one wave length.

The lower ends'of theV first pair Vof antennae, 1, 1 are connected together by Vmeans of bridle wires and the upper endsof the correspondingVV pair ofVv counterpoise elements'2, 2 are connected int-the saineinanner by bridle wires 38. The otherrpair of antennae' and counterpoise elements are also connectedvby'V bridle wires, 39 and 40 in t-he same manner, and further connections 41, 42, 43 and:44 aref provided whereby all of the antennaeelements 1 are in parallel and all of the counterpoise elementsv 2 are in parallel with reference to inductance 3.V

,The specific Ydetails and relative arrange- Y ment of this antennae system are disclosed andclaimed in a 'patent to F. YConrad No. r Y1,689,863 of October 30, 1928, and assigned to, i

the Westinghouse Electric & `Manufacturing Company.

if' Inductance 3` is-coupledto, inductance nsvvysas nvfvlichs connectedby conductorsto the-receiving 'station `amplifier,"as indicated iniFig..

`1. A The i. loop is tuned by `1 condenser 11 fand tofa secondinductance"13connected Lacross -theiwiresmi leading to theyrece-iving station this loopnwill` be explained later.

fampliiierj9. `The `operation and purpose of Figpt lis a `diagrammatic View of thecircuits `and Vapparat/us involved in thereceiving V station amplifier V9,.; ,The first tube of lthis amplifier hasshunted acrossits input circuit 52, 53a crystal 54 tuned to the frequency of `the signals being received. A feed back,or

ticklercoil isvariably coupled to inductance 7 ,and is providedwith a tap 56 at or near its midpoint-leading to a point 57 on the :tuned input circuit58, 59v of the second tube V600i? the. series. Thistube `60 is provided f with ha tuned outputcircuit comprising inductanceffand condenser 63 and is arranged according tothe disclosurecontained in Rice i Ailatent N0.-1,334E,118 so that it will not oscillate spontaneously. Thisfreedom frein osl cillatlon is secured bymeans of the feed-back v d tery 108 and-inductive grid lealr109 connected condenser 64; "The output circuit 62, 63 of the second tube 60 is 'coupled through lead 65 and condenser 66 tothe input `circuit of the thirdtube70, which tube70 `is also shown as "neutralized by condenser I" The owutput'circuit 2, 7 3 of this :third tube 70 `is .coupled to the input circuit of a fourth tube `76thro1`igh lead 4" and condenser 75. The circuits, accompanying `tube 6 are substantiallythe same `as thosevof tubes {S0-and 70,. comprising aV neutralizing condenser `7 7 as well, andffor that reason are not described morespecilically The output` of the last tube 76"of this ,station amplifier is shown as an inductance 161 tuned by condenser 78, and coupled to another finductance 15 shunted across the land Vlines lleading to the trans- ;mitting station` amplifier whichV is shown diagrammatically in Fig. 5.1 y

` Referring now specilically to` Fig. 5,fitwill i be noted that the land lines 16 are tappedinto i `an inductance 18 in the input circuit-of the first tube 82, at points "837 the potentials of which may be predetermined with reference to ground connection 84.! The (purpose of "this type of connectionl will'l be more fully "explained later.

d The Vtuned output circuit 852,86 of tube 82 is coupled tothe input of tube 87 by means of condenser 88, both `of these tubesfbeing neu- Rice Patent referred topreviously by means *of-condensers 89 and 90. The output circuit 913` 92 ofthesecondtube 87 is coupled through -tendensen 9a te agrupar @nella of the third rtube'iHQlfwhich' latter tube` has inits output prising tubes r99 and 100: Connected between the gridfof tube 99`ftof-a'point on the plate circuit oftube -100 isa neutralizing condenser 101', while betweenrthe grid circuit of tube 100 and the plate circuit: of? tube 99 `is va :second neutralizing condenser 102.` Therpurpose-of these condensers is to prevent fthe vpush-pull amplifier from oscillating atlundesired frequencies.l l l y An inductance `103 "shunted byA Condenser y104 forms the'outputcircuit of both of these -1 tubes, and is provided witlracentral'tap'l for the plate supplyl- Coupled to theioutput circuit1103y104, by means of condenser `26fis another' amplifier tubel07, preferably. of the water-cooled high power type. The gridrpotential of theftubei107 isunaintailied `at the best operating` point by means `of(lV batacross between the gridf1-18 `and ilament 11,1. The output circuit1 of the `high power tube 107 comprises a low-loss inductance29 shunted by Aa tuning condenser28,as'shown in Fig. 1 and isv preferably tunedsharplyto: the broadcasting frequency.; This inductance 29 is' coupledto the radiatingsysteml bymeans of the condenser 30.'`

In Fig. 6 is shown a `modified-1 system of connecting the lloop* 10 tothevlines l5 between the receiving antennae and the local' alnpliiier station 9." The loop-is shunted by anlnductance f12 equivalent to the" inductance 12 of Fig. 3, and is also shunted by aftuning condenser 11 and a second inductance120ff A `ductor 5 I connects" the lower' 'portion Vof the coupling inductanc'e- 4 to the mid-point of the inductance`120''and"infseries with this conductor is aniinductance121. This forms what `may be termed aphantom circuit;

Tracingthe path of a signal impulse arisin'gin the'vcoupling in'ductaincellit will be seen that this impulse will' pass :in f both directionsthrough inductance 12 and thatleads 122 and 123 are consequently in parallel with A'reference to such-impulses.'` The' inductnce 121 will therefore be affected only bysignals arisingin the coupling inductance 4 while theinductance` 120 will have in it only signals arisinglinth loop 10';- l

Y An inductance 7 connectedswith the receiving station amplifier 9 may be variably-- coupled to either' inductance` 120 or-{121ho`rwto :bth offsuch inductances simultaneously", thus 'fis - output circuits; The input circuit of the first tube 13()V comprises a choke coil '131 and a C'battery 132 shuntedrbyna crystal 1,33 ground vto have aVv definite vfrequency- `By tuning the output circuit'134, 135 of'this first tube tothe crystal frequency,oscillations may be set up therein, Whichare impressed on the grid circuit of thc'second tube136 through condenser 137. The outputcircuit 138,139 of this secondv tube 13.6 is Vtuned tol a harmonic of the Vfrequency generatedby the first tube 130 and is, in turn,-coupled lby condenser 140 to the input circuit of still anotherltube 141 Whose outputcircuit 142, 143 is tuned to a harmonic vofV the frequency emphasized bythe secondr tube. Y Y It vvillthus be seen that, by properly choosingvthe crystalshunting the first tube input, and by correctly tunin-gthe successive out'- put circuits, anyfdesired frequency finay be obtained in the output circuit of the. lasttiibe of the series.- This `last tube may be arWatercooled high-povvertube or anmnber of suchV tubes in parallel, and the amplifier-tubes shown in theoth-er positions are merely indicative of the'manner in Which the oscillation generator is constructed.V l

1 This type of crystal-controlled oscillation generator is disclosed and claimed;incopend` ing application of Donald Gr. Little, Serial NO. 78,115, filedfDec. 29, 1925, and assigned to the Westinghouse Electric Manufacturing Company L Referring specifically to Fig.' 8, thisfvieW illustrates diagrammatically hoW the oscillation generator shovvn'in Fig. 7 may be substituted for the simplev crystal control of Fig. `4.V With this arrangement, thereis no neces- Y sity' for 'employing thefeed-back coil 55 as Y As in Fig. 4,*.thetub'e 50lhas a'tiinedi'input the oscillationV generator, 'which is .arranged Ato give an Voutput vat the Iincoming frequency, supplies enough energy to-make up vfor circuit losses.A

circuitcomprising aninductance 7 and con- Y denser 17'..` .The inductance 7 is connected-by 'leads 144 an`d145,7to thel oscillation generator indicated 'by rectangle 146. :This tub-e 50 .is

rovided further With a `tuned output lcir- `cuit.147,'148, Which is connected by leads 149 'and 150 to thev neXtl amplifier stage, which may be essentially as shown'in Fig. Having Vdescribed the .specific elements eini' bodied in .my improved relay system, Ythe' op'- 'eration thereoftwill no'vv be described-' l; y.Referring.again.to Fig.'-.1, the pathof aVV signal wiii be' traced' @intagli the'cnipite system.. An incoming signal, vafter havingV lbeen received on the .antenna system" 1, 2

shown in detailin Fig.Y 3, is transferredto the lines' 5 leading from the coupling rinductance "4to the receivingstationv amplifier 9. This antenna'system-l-EZ is so arranged and pro'- portioned that signals .coming from a direction parallel to the line of A-B the antenna i poles, indicated in-Fig. 3, tendto cancel out inthe coupling coi13 being out of phase in vthe several sections "off Ythe antenna which are tied together Vby the bridle Wires 41,V 42 and 43, 44. rlhis characteristic is fully explained in the copending application ofv Conrad above referredtoL Y y Onthe other hand,-signals coming fronfr-a reinforced. Obviously, ,thej receiving an- VVdirection perpendicular to the antennav line are received in the saine-phase in analogous sections ofthe antenna and are consequently tennae Will pick up a small amount Ofsignal from the local transmitting station and for this reason the loop 10, which has highly directional characteristics, is used toV balance out this' local signal.

After having been amplifiedat radio frequency, ,the signals are transferred to land `,lines 16,' F igs.4 and 5,1by'ineans ofcoupling inductances 14,15, Which land lines'are con-f nected to an input Vinductance l'forming'aV part of the receiving station amplifier. p

It Will be noted from an inspection of Fig.

Y'fthatthegfilarnent.circuit of the LirstftransH initting station amplifier tube 824is` grounded at 84 and that the land lines 16 areconnected to the input induct'ance 18 of this'tube in such manner that' each of these lines may be mainjtained atfthe saine potential with respect to ground. This result is accoinplished'by mov- Vable contacts 83. means of this connection, the land lines are prevented to a largel c xtent from radiating energy and at the saine time any energypicked up by these land lines tends to cancel in the inductance 18. VvThis manner of connection secures a very important result, i. e., the "prevention of'fe'edback amplifierl 19,

Vfromsuch lines to the receiving antenna andn the elimination ofpicl-up by tlie'se'liiies of Athe locally radiated signal 'i Y Y In they transmitting station 24,27, the incoming high'freque'ncy'signalfis repeatedly amplified@ but its frequency is not changed. "'Thisfaniplifier, as eiqplained'in` connection with thedescription of Fig. 5

employs tubes of successively higher powers,

Tn 'the construction of this amplifier, great l difiiculty Was at first experienced.dueto'feedback between the various units thereoflpa'nd 1 y consequent undesired escillation.-

Afeed back is y. obviated-V in the lfollowing f manner Y .i

.The .output indu'ctance 2O of the first section of v'thel transmitting station amplifier is connected by means Vof coupling condensers. 21

" choke coils Whichserve as gridleaks.

cuits in paralleland their output circuitscomprising portion of a single inductance 103. `The inductances 97 and 98 shown .as connected across the input circuits of, these two `power ampliflertubes are high frequency explained before,` this power amplifier is l l neutralized according to the teachings of the iRioePatent 1,334,118 to prevent parasitic oscillations.

f" "The filament circuit f this power amplifier hasa ground connection y125.` The central point ofthe coil ismaintained at ground potential, as far as regards the radio-fre- M quency urrents." The leads 113 are "connected 10n tolpoints of the coil 20 symmetrically situated i as regards said central point. Consequently, the 'radio-frequency potential between either lead 113 and the ground is of the same amplitude for each lead. If, from any cause, an

Aextraneous potential difference between the groundland the'amplifierf is present, it will aEect the two leads 113 in the same way. disturbance picked up `by these leads bein phase'in each"` and" will cause the 0' grids of the amplifiertubes to vary synchronously as to potential. `The `currents in the-output inductance will accordingly be in `opposite directions so there will be no tend-4 A.. ency for `an oscillatingcurrent to be set up l in the circuit comprising the inductance 103 4andcondenser 104. .This arrangement nullies the effects of undesired energy pickedup by leads 113 from eitherthe transmitting antenna or other portions of the amplifier. On 0T the other hand,. when signals are impressed on the input circuits of this power amplifier through coupling leads 113, it is obvious that the grids will acquire charges differing in potential. `The net affect ofsuch differences 5 will beto set up a circulating current in the circuit vcomprising inductance 103 and condenser 104. This output circuit is coupled to the input circuit of a power tube 107 by means i), of a coupling condenser. The output circuit of this tube 107 is formed by an inductance' 29 and a condenser 28 constructed to have minimum losses and is commonly known asl a tank circuit. This circuit is very carefully 51' tuned `to the broadcasting frequency and` is coupled through condenser 30to the radiating system 31. This general type of coupling isfdisclosed and claimed 4in the patent to Ff Conrad, No.` 1,652,516 of December 13, 1927,

:el and aSsignedtothe Westinghouse' Electric 8a,

Manufacturing Company. y

Incoming signals are` accordingly re-radi atedffrom Vthe `local transmitter still at the p frequencyreceived. YThe various amplified i5" stages haveno4 `function other l than that of increasing the amplitude of an extremely Y weak signal until yit is suiiiciently powerful'to be Are-radiated. i

In order to insure that even the weakest of received signals may be re-radiated with maximum intensity, I mayfmake use of a regenerative receiver operating on the homodyne prlnclple.

VReferring again to Fig. fl, the first tube is equipped with a tuned input circuit comprising inductance 7 and condenser 17 and coupled to this inductance 7 another in'- ductance in the plate circuit of the tube. Y This forms a tickler re-generative arrangement andthe coupling between these inductances may be made so close that this tube will generate oscillations. The oscillations lenerated by this tube are repeatedly amplified as they pass through the whole system andare eventually re-radiatedfrom antenna 31.

\ In order to secure a constant frequency of radiation this first tube 50 is shown ashaving a piezo crystal 54shunted across its input cir-- cuit 52, 53.0 This crystal serves to maintain the frequencyof oscillationsof this tube substantially constantso that variations in thetuning of the antennacircuit occasioned by wind, etc., will not appreciably `affect theL frequency being re-radiatedfrom the transmitting station. The frequency to which the crystal 54is ground should be the same as that of the signal it is intended to receive. This ensures that the resradiated frequency will be thesalne as the frequency sent out by the master station. i

l The crystal shown may be, if desired,'re'- placed byl the type of oscillation generator shown in Fig. 7 and previously described. The manner in which" such oscillation generator may be employedis shown in Fig. 8 and has also been described.

' In the event that the signals being received from the master station, or from neighboring relay stations, are of suiicient intensity, the tickler coil 55 and crystal control 511 may be omitted from Vthe first` section of the amplifier shown inFig. 4. VWith these omissions, the tendency toward self-oscillation in the amplier' is lessened, and, in many instances, theniodulation ofthe transmitter output is improved.

Another and very important phase ofmy invention, which is illustrated in Fig. 2, deals with 'the `pr0blemof interference bythe locally received sivnals and the locally transmitted signals. In most previous attenflptsl at relaying, considerable difficulty has been experienced byreason `of the receiving antennac picking. up such a large proportion of the locally radiated energy as to seriously aifectothe` lreception. I have, by means of my invention, entirely obviated this defect. The receiving antenna as shown somewhat in detail in Fig.` 3 and described and claimed `l 'sli its

rio

antennze therefore, pick up buty a small 1928, has very pronounced directional characteristics. As indicated by polardiagram 32 the reception in the direction of a line' A-B parallel to the antenna poles is quite poor, whileireception on a line normal there-1 to is'eXtiemely good. The transmitting ane.

tenna is shown at 81 and is so arranged that all of the separate antenna unit's,zboth of the .receiving i and of the transmittingY antennae, arein alignment. 'i

It will be noted that the transmitting antennae consist of four sections, each of which, in practice, is composed of a vertical antenna and counterpoise connected through an iiiductance. "These sections are horizontally separated by distances corresponding to definite fractions of the wave length, A, to be received, as shown inV the diagram.L The antenna sections 31 in line with the receiving antenna Aare each separated by a distance equal to one-half of the wave length being received in meters,wl1ile another antennaV` section` 31 is separated froin the line-up a distance equal to one-fourth of a wave length. Situated a distance one-half wavelength from the receiving antenna line-up is a'loop rotatableabout-a vertical axis, the polar diagram of'which isfshown at 33. Atonehalf wave length from this loop is located the receiving station containing the receiving amplifier apparatus and circuits as illustrated in -.Fig. 1. The purpose of this spacing is to secure a better balance in the received signals from the source showny at 1, 2andy is fully explained and claimed in'myV copendingV application referred to above.,

As will be seen from the polar diagrams of the receiving and transmitting antennae, the

l lines of-best reception and transmission are paralleler approximately so'. The receiving amount of energy from the transmitting antennae, which latter may besituated a num` ber of miles away. This smallV amount of energy is nevertheless troublesome and the loop 10-is accordingly used to balance'out such energy by introducing into the transl l mission line, as shown Vin Fig. 3, an kequal amount ofenergy 180 fout of phase therewith. This relative arrangement of receiving and transmitting antennae together with the position ofthe balancing loop'wth respect to ther-direction from which signals are de` s ired,ris an important partof my invention. It will thus be seen that by employing my4 i invention in connection with broadcasting of intelligence, marked economy of operation y maybe attained. A; single high power station .isv enabled to control simultaneously, a large number Iof'relay stations and each relay station, in turn, .serves to augment` the power.v being sent' out'by the first station.

All of tliestations in the system will operate,f

on' 'the same wave length-and Vit is obviousA that eventhough there be some stationsloc-Y yond the frange of rtlieinaster br control' station, the VVenergy sent out by near-byfrelay stationswill be tant stations.

A minimum of trained men'is required to operateeach separate relay station as my system whenV once adjusted, is practically automatic in its' operation. Y

herein vcertainspecific embodiments of my inventionI am fully aware that within the bounds of such invention many other modifications are possible, and I do not desire to` be limitedjexceptin so far as is necessitated bythe prior'artV and by the spirit of the foll lowing claims.V Y

Y Ilclaim asmy invention:

A 1.1 In combination,- a' source of radiant en ergy, means LVadapted to receive such energy,

said means comprising a plurality of substantially vertical conductors geographically situated alonga line Vnormal to the directionfrom which the energy is received, a secondsource of radiant energy controlled by said receiving means, said second source being also located on the same line normal to the direction from which energy is received, and additional means, .comprising a loop-antenna, for pre# venting said secondV source from interferring-V with the reception of signals Aby the receiving means., Y 1 Y g Y i 2. In -a radio relay-system,'means for..im-4

pressingreceived radiant energy on` a vacuum mentioned amplifier to .the inputfcircuit of the` secondV amplifier, and 'means formaintaining the conductors constituting said line, and the homologous parts of said last-ment1oned am-V sufiicient to operate suchV dis! Although' Li have iiiustmtea .and desc'fibea Wiz:

plifier Aat leqiiz'il effective potentials with ree l spe'ct to ground.

1. In combination, an amplifier having an output circuit including an inductan'ce, a second inductance, aV plurality of' vacuum-tube devices connected inpush-pull relation to the second inductance, and circuit connections,

fromrth'e first inductance to separated points on the second inductance at equal eective potentials with respect'to ground, whereby radiation from circuit connections is minimized;

5.- In an amplifying system, a vacuum-tube device having a cathode, a grid and an anode, an inductance connected at one terminal to saidfanode and'at its other terminal tothe grid, `a capacity included in the last named connection, .a second inductance, a plurality of vacuum-tube devices connected in push- "pull relationship to saidsecond inductance, and connections from the first inductance to separated points on the second inductance at equal effective potentials with respect to ground. w

` 6. In a relay system, a radio signal receiver, an amplier for the received signals, a radio transmitter situated at a distance from said signal receiver, connections between said radio transmitter and' saidVV amplifier, and means whereby sai d-connectlons may be maintained atequalleective potentials with respect to groundinsofar as potentials impressed thereon vfrom said transmitter are concerned, whereby parasitic oscillations are prevented from being set up 1n said system by reason of feed-back from'said transmitter. y 7.- In a radio' relay system, means Lforrei ceiving signals, means for amplifying the received signals, said amplifying means Vcomprising units separated a substantial distance apart, means for re-radiating the amplified signals, circuit-connections between the receiving means, the amplifying means and the radiating means,fand means whereby the connections uniting spaceseparated units of the amplifying means arevrestrained from radiating.

y 8. In combination, a directional receiving `antenna system, a directional trasmitting ani tenna system so arranged that the direction ofmaximum reception of the receiving antenna system is substantially parallel tothe drectionof maximum radiation of the transmitting antenna system, and means comprising a movable loop for minimizing the effect of the transmitting antenna system on the receiving :antenna system.

9. In aeradio relay system, a receiving an- -tenna having a non-uniform directional characteristic, a transmitting antenna located in a direction from thereceiving antenna in i which the receiving antenna has a minimum eii'ectiveness, a supplemental receiving antenna having, an adjustable non-uniform directional characteristic and means for superposingthe energy received by said supplemental antenna upon the energy delivered to the receiving antenna by the transmitting antenna ina `directin to tend to counteract it, whereby adjustment of the directional characteristic of said supplemental antenna may cause said counteracting to be complete.

. In testimonywhereof, I have hereunto subscribed my name this 26th day of January,

. FRANK CONRAD. 

